1. Field of the Invention
The present invention pertains to monitoring systems and more particularly to systems used to monitor many locations using only one sensor where the sensor is selective to monitor a single substance.
1. Related Prior Art
Present technology has illustrated several different methods for detecting unwanted leaks of environmentally destructive substances. The following patent is representative of a chemical/mechanical detection and warning system.
U.S. Pat. No. 4,590,462, titled "Oil Leakage Detection Apparatus", issued to Robert M. Moorhead relates to a chemically activated rotary actuator mechanism which reacts to exposure to hydrocarbons such as gasoline and oil. A detected leaks causes a rotor to forcibly rotate from a rest or static position. Spring members are used to load the rotor with, compressive forces which act through the rotational axis of the rotor to cause the mechanism to be unstable in the static position. The rotor is rotatably mounted in a body member and constrained from rotation with respect to the body member by means of shear pins which degrade when exposed to hydrocarbons. Rotation of the rotor shaft is utilized in generating an alarm.
Present technology has developed several different methods for using fiber optic cables. The following United States patents illustrate how the sensitivity and transmission qualities of fiber optic cables can be affected.
U.S. Pat. No. 4,270,049, titled "Liquid Leakage Detection System", issued to Masaya Tanaka et al. relates to a method for detecting a leakage of a liquid in terms of the drop in intensity of light rays traveling through a light guide core or optical fiber made of glass or synthetic resins. The change in intensity is due to the adhesion of the leaked liquid to the light guide.
U.S. Pat. No. 4,634,856, titled "Fiber Optic Moisture Sensor with Moisture-Absorbing Reflective Target", issued to Randy R. Kirkham relates to a method and apparatus for sensing moisture changes by utilizing optical fiber technology. One embodiment uses a reflective target at the end of an optical fiber. The reflectance of the target varies with its moisture content and can be detected by a remote unit at the opposite end of the fiber. A second embodiment utilizes changes in light loss along the fiber length. This can be attributed to changes in reflectance of cladding material as a function of its moisture content. It can also be affected by holes or inserts interposed in the cladding material and/or fiber. Changing light levels can also be coupled from one fiber to another in an assembly of fibers as a function of varying moisture content in their overlapping lengths of cladding material.
U.S. Pat. No. 4,710,353, titled "Corrosive Liquid Leak Detecting Sensor", issued to Satoshi Tanaka et al. relates to a detector for detecting leaks of a corrosive liquid such as strong acids or bases. This detector includes a light guide core having a covering which generates heat upon contact with the liquid to the detected, thereby changing the light transmissivity of the light guide which can be measured. The covering comprises a porous polymer having a salt within its pores such as an ammonium salt which dissolves in the liquid to be detected and generates heat.